When Coco Gauff, 15, broke onto the scene at Wimbledon, one quality shone above all others in her game. She has the ability to grind out points, to push past errors and find a way to secure a win. Her United States Open debut on Tuesday, a victory over Anastasia Potapova in three sets, had a similar feeling to it.

Although she committed 42 unforced errors and had only 14 winners in the match, Gauff returned 88 percent of Potapova’s serves and put the pressure back on the young Russian.

On Thursday at 7 p.m. at Louis Armstrong Stadium, Gauff will face Timea Babos, a qualifier who has won two Grand Slam doubles titles — at the Australian Open in 2018 and at the French Open this year. Babos, a veteran Hungarian player known for her consistency, may be the perfect test for Gauff to see how she can overcome her game’s own inconsistencies.

Because of rain, only nine singles matches were completed Wednesday. That means Thursday’s schedule is packed with 54 second-round singles matches and an assortment of doubles and mixed doubles. — Max Gendler

Matches to Watch

Rafael Nadal vs. Thanasi Kokkinakis (night session)

In his news conference Tuesday, Nadal jokingly referenced his injury history, saying: “I have the same body. Well, I would love a new body, but not possible for the moment.” If Tuesday’s straight-set victory over John Millman was any indication, Nadal’s old body can still do the job quite well. Nadal called Kokkinakis, a 23-year-old Australian, a “dangerous opponent.” But the two last met at the 2014 Australian Open, where Nadal won handily, and Kokkinakis has struggled with injuries in 2019.

Coco Gauff vs. Timea Babos (night session)

In her United States Open debut, Gauff, the 15-year-old American phenom from Delray Beach, Fla., fought back after a shaky start to defeat another talented teenager, Anastasia Potapova of Russia, in the first round, 3-6, 6-2, 6-4. “I think this is the first match where people actually had a chant for me, so that was pretty cool,” she said after her win. Her next chance to bring the U.S. Open crowd to its feet: a second-round match against the veteran qualifier Timea Babos.

The Most Exciting Moments (So Far)

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Thomas Fabbiano after upsetting Dominic Thiem at the U.S. Open on Tuesday. CreditJustin Lane/EPA, via Shutterstock

Four Top-Ten Seeds Lose

On Tuesday, No. 4. Dominic Thiem, No. 8 Stefanos Tsitsipas, No. 9 Karen Khachanov and No. 10 Roberto Bautista Agut were knocked out of the Open in the first round. Thiem bowed out in four sets, falling, 6-4, 3-6, 6-3, 6-2, to 87th-ranked Thomas Fabbiano of Italy in Arthur Ashe Stadium. Tsitsipas also lost in four sets to the in-form Andrey Rublev, a 43rd-ranked Russian who defeated Federer at the Cincinnati Masters this month. Bautista, who was the non-Big Three semifinalist at Wimbledon this year, lost in five sets to 47th-ranked Mikhail Kukushkin of Kazakhstan. Khachanov fell in five sets to the 216th-ranked Vasek Pospisil.

Serena Williams Defeats Caty McNally

Caty McNally made it clear very quickly that Williams, a 23-time Grand Slam singles champion, was in for a serious challenge on Wednesday. “I felt really good out there on the big stage; I wasn’t too nervous,” McNally, a 17-year-old American, said. As Christopher Clarey writes: “It was a classic Williams performance. She has turned so many tricky matches her way through the decades: first against her elders and now against new arrivals not even half her age.”

Top-Seeded Naomi Osaka Advances

Osaka battled her nerves in a three-set, first-round win on Tuesday. Two days later, Osaka, who is wearing a brace on her injured left knee, shook out her leg several times because of apparent discomfort. Playing in front of a star-studded support box that included Kobe Bryant and Colin Kaepernick, she advanced to the third round with a 6-2, 6-4 win over Magda Linette, who won the Bronx Open last week. Osaka awaits either Timea Babos or the teenage phenom Coco Gauff in the third round.

Pop Quiz: U.S. Open Edition

We know our readers are avid sports fans. So we’re going to start putting you to the test. This week, see if you know the answer to this question, from Ben Rothenberg.

Denis Kudla will play a third consecutive Serbian opponent when he faces Novak Djokovic on Friday. Venus Williams beat two Serbs in a row on her way to the 2007 semifinals. Who were they?

Last week’s correct answer? The winning quarterback of the X.F.L. championship at the end of its only season in 2001 was Tommy Maddox. The first reader to answer correctly was Jonathan Jacoby, who sent the answer in two minutes flat. We salute you.

Email your answer to sportsnewsletter@nytimes.com. First person to send in the correct answer gets a shout-out next week.

A Good (Competitor) Read

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Rich, left, and Tom McEvily were ball boys at the first U.S. Open in 1968 and say it was the “best job we ever had.”CreditEarl Wilson/The New York Times

These days, if you want to become a “ball person,” you have to survive a very involved tryout process. In 2015, the GQ writer Freddie Campion (to be clear — a 29-year-old at the time) tried to make the cut.

He wrote about his experience — which includes hitting another ball person with a baseball — here.